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    Why there was No Lunars Era
    From: Alexandre Eremenko
    Date: 2004 Dec 7, 15:03 -0500

    The original question of Frank was
    (as I understand it)
    why there was no Lunars era?
    We were explained that there WAS a Lunars era
    in the LAND navigation,
    so it remains to find out why there was no
    Lunars era in marine navigation.
    My first guesses were:
    a) low precision (because of difficulty of measuring
    distances better than 1') and
    b) difficulty of reduction
    These guesses were refuted. I accept this,
    and will return to this in
    the end of this message.
    Here is my second guess.
    Roughly speaking "Who cares about longitude in marine navigation?"
    I apologise in advance: I mean European and N American marine
    navigation (not the Polynesian, Chinese or African ones).
    In the seas like Black sea or even Mediterranean and Baltic
    you can probably do well enough with DR only.
    In the coastal waters ("cabotage") no CelNav is needed
    if you gave good maps.
    So we are talking of ocean crossings.
    But most of the ocean crossings occur E to W (or W to E)
    don't they?
    So it is enough to know your latitude to reach the point you
    want in a typical ocean crossing.
    One supporting argument is that there were very many successfull
    ocean crosings before the "Longitude problem" was solved:-)
    One interesting exception is polar navigation in the
    "NW passage". I combed the Franklin notebooks on this subject.
    He mainly used chronometers, though occasional lunars
    were mentioned too.
    This is the main part of my message.
    Now about the refutation of a) and b) in the beginning.
    1. My complains about difficulty of reduction were mostly
    based on a misunderstanding. My misunderstanding.
    I have no horizon. I had to compute altitudes every time
    I reduced my lunars. Which I did
    with the usual formulas and a calculator.
    Of course if you subtract this
    a lunars computation becomes much easier.
    2. Precision. Those members of the list who replied my questions
    say essentially that they can measure distances to 0.3', and
    get such results on a regular basis. So far I can do it only
    to 0.6' on a regular basis, but they say one needs at least 10
    years experience to measure the distances well on a regular basis,
    so I still have 9.5 years to practice:-)
    My main problem is in determining precisely when do two discs
    touch. This is the sort of problem which is
    "hard to address in words" as Bill noticed once.

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